If you have recently tried to upgrade to Debezium 2.3.1.Final, you may have found when using the SQL Server connector that you received an unusual error when starting the connector which said, "Configuration query.fetch.size is defined twice."

Unfortunately, this error was not intended and there is no workaround to remedy the issue. Thankfully, Debezium 2.3.2.Final is here to the recue; this release addresses this regression, allowing SQL Server connectors to start once again. If you are looking to upgrade, and you rely on the SQL Server connector, we strongly recommend that you avoid the 2.3.1.Final build and instead move directly to 2.3.2.Final.

Debezium uses JDBC in order to communicate with the Oracle database. The Debezium for Oracle connector relies on two configuration properties, snapshot.fetch.size and query.fetch.size to control how much data is returned for a query on each database "fetch" call.

When these properties are configured too low, this can cause Debezium to perform more network round trips to the database to read data and that network latency can add up, particularly when working with large result sets. When these properties are configured too high, this can cause Debezium to consume more memory, but reduces the network latency incurred for the fetch round trips to the database. Ultimately, it’s important to strike a good balance based both on the what your ideal data size may be but also based on the memory and hardware constraints of your environment.

While discussing performance with one community member, we concluded that adjusting these values from their default of 2000 to 10000 increased the connector’s throughput quite substantially for their environment. So in this release, we felt it made logical sense to consider increasing the default to 10000 to provide a better out-of-the-box experience for Oracle connector users.

Now, these configuration properties are performance tuning knobs, and unfortunately there isn’t a guarantee that what works well for some environments is going to necessarily be universally good. Please take note of this change and if you experience any issues, you can always set the snapshot.fetch.size and query.fetch.size properties in your connector configuration, even setting them back to their previous default of 2000 if necessary.

Debezium 2.3.2.Final also includes quite a number of bug fixes and stability improvements, see below:

Please refer to the release notes to learn more about all fixed bugs, update procedures, etc.

Many thanks to the following individuals from the community who contributed to Debezium 2.3.2.Final: Bob Roldan, Chris Cranford, Indra Shukla, Jiri Pechanec, Jochen Schalanda, Robert Roldan, Vojtech Juranek, Yashashree Chopada, faihofu, j2gg0s, and paul cheung!

A great deal of work has already gone into the new preview release of Debezium 2.4. We plan to do the next Alpha2 build in the middle of next week, which will include a plethora of new features and improvements. There is still time to share your feedback and suggestions if there are things you’d like to see in 2.4, so take a look at our road map and reach out on the mailing list or our chat.

Finally, Debezium 2.3 will continue to receive maintenance updates. We’ll likely release 2.3.3.Final later in the month barring the community feedback on regressions and bug fixes.